Burden of Disease

Holstein calf laying in the grass and looking right at the camera.

An area of interest to me that falls outside our normal frequency measures of disease is the concept of summary measures of health. I am lucky to have had colleagues and dairy producers both at CSU and here at WSU who have been interested and supportive of research into this area. We have published on this concept (Prev Vet Med. 2017. 1431; Ir Vet J. 2018. 712) and continue to research burdens of disease through objective disability weight measures3 and additive effects of disease sequelae. Although our initial forays into burdens of disease were focused on adult dairy cattle, recently we have been working to quantify the burdens within calves and attempting to establish the long-term effects on productivity, longevity, and subsequent disease responses.

This concept has attracted other researchers as well, and two recent publications highlight the application of disability weights and measures of the burden of disease within calves. Ramos et al. initially set out to develop calf disability weights using the opinions of producers and veterinarians (J Dairy Sci. 2025. 108. 34). Briefly, disability weights are meant to serve as a measure of the severity of a particular health state. They were initially employed in the Global Burden of Diseases, Injuries, and Risk Factors project for humans (Global Burden of Disease Study 20195), and applied as part of the Disability-adjusted life year (DALY) metric which is used to measure the overall burden of disease, disability, and premature mortality. It combines the years of life lost due to premature death (YLL) with the years lived with disability (YLD). For the Ramos study, a visual analog scale was used to estimate the impact (0 = no impact; 10 = death) of 9 frequent diseases or syndromes (diarrhea, dystocia, inadequate transfer of passive immunity, fracture, wound or abscess, arthritis, respiratory disease, umbilical infection, and congenital defect) on calf health. The highest average impacts were obtained for the presence of a fracture (6.49/10), arthritis (6.22/10), and congenital defects (6.03/10), whereas the lowest impact was observed for the presence of a wound or abscess (3.42/10). The opinions of producers and veterinarians were similar for most of the selected diseases and syndromes; however, statistical differences were observed for arthritis (producers = 5.13 vs. veterinarians = 6.88), umbilical infection (producers = 3.65 vs. veterinarians = 4.74), and dystocia (producers = 3.87 vs. veterinarians = 4.58). These differences in opinion are not surprising given the varied individual experiences people have managing calf disease. In fact, such differences underlie our own current efforts to quantify dairy disability weights through objective measures of pathophysiological outcomes. Nonetheless, in the Ramos study producers and veterinarians mostly agreed on the impact of frequent diseases and syndromes affecting calf health. The resulting disability weight estimates provided the first step in creating a health measure for dairy calves for comparative health analyses for producers, veterinarians, and industry.

In a follow-up study just published (J Dairy Sci. 2025. 108. 106), Ramos et al. continue the conversation by assessing the burden of disease and syndromes in preweaned dairy calves using the DALY approach. The DALY estimates were obtained as per human metrics by summing the YLD and YLL. The previously reported disability weights for frequent diseases and syndromes were multiplied by their prevalence in the selected farms to obtain the YLD. The number of deaths was multiplied by the life expectancy of a calf in the preweaning period to obtain the YLL. Furthermore, the authors evaluated the association between the DALY and inadequate transfer of passive immunity (ITPI).

Relevant findings were as follows:

  • The highest prevalence of disease and syndromes at the farm level was reported for diarrhea (28.6%), whereas the leading cause of calf death was dystocia (33.8%).
  • A median of 2.03 YLD/10 calves was estimated for all 40 dairy farms. For those farms that reported mortality data (n = 30), a median of 1.46 YLL/10 calvings and 3.37 DALY/10 calves-calvings per herd were observed.
  • The main causes of health losses related to YLD were diarrhea (1.46) and respiratory disease (0.42).
  • In general, ITPI was significantly associated with YLL (Spearman’s r = 0.43) and DALY (Spearman’s r = 0.41).

The authors ultimately state that the DALY showed a viable approach to combining information on morbidity (including different diseases) and mortality in a common metric for dairy calves. They suggest that the DALY could help producers and veterinarians in the identification of health priorities for preweaning dairy calves. I agree and would add the following considerations based on our own work in this area.

  • Given that most calf morbidity is related to gastrointestinal (GI) and respiratory disease, a conversation regarding disability weights specifically and the DALY in general should incorporate refined case definitions. For example, consider adjusting records and outcomes to acknowledge that not all diarrhea (a symptom) is reflective of the same severity of GI disease. Disability weights can account for this and create space for capturing systemic versus local disease states.
  • Although GI and respiratory disease are overrepresented in calves, adult cattle are more prone to a suite of diseases whose frequencies often align with specific period of lactation. Early lactation morbidity and mortality may have an outsized impact on productive life but be masked by more frequent but less detrimental disease states later in the lactation. The DALY concept allows those various disease states to be framed as lost days, years, or lactations which may be more comprehensible than using frequency measures alone.
  • It is important to emphasize that a summary measure of dairy health goes beyond simply linking morbidity to culling and mortality in a standardized fashion. A summary measure speaks to the burden of disease on both the well-being and productivity of individuals and populations. Such an alternative accounting of disease highlights the lost opportunity costs of production as well as the burden of disease on life as a whole. 

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